The invention concerns a powder device for powdering printed sheets, comprising a powder container containing powder and from which powder is extracted, wherein the powder device is designed as an exchangeable container which can be removed from the powder device and which has an opening at its lower end which can be closed by a closing element.
There are a plurality of conventional powder devices of this kind. DE 22 52 474 A discloses e.g. a supply container for powder, wherein the lower opening forming the outlet can be closed by a ball. Containers of this type have, however, the essential disadvantage that they are relatively easily blocked, since the powder sticks to the side walls or powder bridges are formed thus preventing further supply of powder from above. GB 15 88 393 B discloses a container having an elastic bottom which is moved via a vibrator. The powder is not drawn off from this container via a lower flow opening, rather suctioned off using a suction air flow. This also has the above-mentioned disadvantages, since the powder adheres, in particular, to the walls and can no longer continue to flow towards the suction nozzle. U.S. Pat. No. 4,051,981 discloses a powder device having a bellows-like supply container, opening into a pin-cushion from which powder can be blown into a blowpipe by compressing the supply container. This device prevents sticking or formation of powder bridges, since the supply container is continuously elastically deformed.
DE 38 11 309 also discloses a supply container for powder, wherein the lower outlet opening is closed by a ball. When powder is required, the ball is pushed into the supply container by an actuating element to loosen up the powder located above the ball which can then flow past the ball in the direction of the outlet opening. Compressed air is blown into the supply container to further loosen up the powder. The container must be sealed in an air-tight manner to prevent the powder from escaping from the supply container.
It is the underlying purpose of the invention to provide an exchangeable powder container which reduces powder build-up on the container walls and which reduces powder bridge formation in the container.